When wearing a monocular head-worn display (HWD), such as in an Air Force simulation and training environment, one eye views the HWD symbology while both eyes view a simulated out-the-window (OTW) scene. This may create interocular differences in image characteristics that could disrupt binocular vision by provoking visual suppression (i.e., binocular rivalry), thus reducing visibility of the OTW scene, monocular symbology, or both. However, binocular fusion of the OTW scene may mitigate against the occurrence of visual suppression, a hypothesis that was investigated in this study. Across two experiments the effects of optic flow rate and target contrast on visual suppression were also investigated. For each experiment, observers viewed a simulated OTW scene and HWD symbology while performing a target recognition task under three viewing conditions. In a partial-fusion condition, observers viewed the OTW scene with both eyes and the symbology with only one eye. In a no-fusion (dichoptic) condition, observers viewed the OTW scene and symbology with different eyes. In a full-fusion control condition, both the OTW scene and symbology were viewed with both eyes. Elevation in duration threshold for a briefly-presented target served as a measure of suppression. The results revealed that, compared to the full-fusion condition, thresholds were elevated for the partial-fusion condition, but to a lesser extent than the no-fusion condition. Increasing target contrast produced less suppression while increasing optic flow rate produced greater suppression. We conclude that under conditions that simulate a semi-transparent monocular HWD, binocular rivalry is present.